The Bcl-2 family proteins are key regulators of programmed cell death, in health and major human diseases, including cancer and HIV-AIDS. Their pro- or anti-apoptotic functions are regulated by subcellular location, as the proteins cycle between soluble and membrane-bound forms;by dimerization with other Bcl-2 family members;by binding to other non-homologous proteins;and by formation of membrane pores that are believed to regulate apoptosis by perturbing mitochondrial physiology. Despite their antagonistic activities, the solution structures of several pro- and anti-apoptotic Bcl-2 family members are very similar, and provide incomplete insights to their mechanisms of action. Most of the structural and functional studies have focused on soluble truncated Bcl-2 proteins, lacking the C-terminal 20-residue hydrophobic domain, which is present in many of the family members and important for membrane targeting. The structures of the membrane-associated proteins are not known, but are anticipated to provide important insights to the mechanism of apoptosis regulation by Bcl-2 proteins. The overall goal of this research project is to determine the structures of the membrane-associated, full-length, Bcl-2 family proteins. We propose a structure-function based strategy that combines NMR structure determination in lipid environments with biological assays carried out in parallel with structure determination. Once we accomplish these goals we will be able to examine the structural consequences of modifications (mutations, cleavage, phosphorylation, myristoylation) and interactions (with other Bcl-2 proteins;with non-homologous partners), as we attempt to further understand the structural basis for apoptosis induction and cytoprotection by Bcl-2 family proteins.